1. Field of the Invention
The present invention relates to a two-sided printed circuit board on which electronic devices are mounted, a multi-layered printed circuit board including such a two-sided printed circuit board, and a method for producing the same.
2. Description of the Related Art
Recently, electronic devices have been progressively enhanced in performance and reduced in size. In accordance with such developments, a circuit board having a larger number of conductive layers patterned to be circuits (hereinafter, referred to as the "circuit conductive layer") and having a larger number of electronic devices in an area unit has been demanded. An example of a conventional circuit board is a multi-layered printed circuit board including a base formed of a resin such as glass epoxy resin. In such a circuit board, a plurality of circuit conductive layers are electrically connected to each other vertically via plating on inner walls of through-holes formed in the circuit board. In this specification, such connection is referred to as the "conventional through-hole connection".
In order to realize a conventional through-hole connection, through-holes should be formed to run from a top surface to a bottom surface of the printed circuit board. In a multi-layered printed circuit board including a plurality of printed circuit boards with such through-holes, it is impossible to realize connection between arbitrary conductive layers, namely "inner via hole connections". Accordingly, a plurality of electronic devices such as ICs provided on the printed circuit boards cannot be connected by a shortest possible distance. In such a structure, electronic devices cannot be arranged with a high density.
Further, with such conventional through-hole connections, a complicated circuit having a great number of nets or a large scale cannot be reduced in size due to a great number of through-holes required.
By contrast, in a multi-layered printed circuit board including a ceramic substrate, an inner via hole connection is realized. However, a ceramic base is expensive, and further production of a large size ceramic substrate is difficult. For these reasons, ceramic bases are not widely used in practical application.